Biochemistry of the Sliding Filament Model

• Myosin head attaches to actin filaments forming cross-bridge

• Head group bends, thin filament pulled along to overlap more with thick thilament.
  -This is the Power Stroke!
  -ADP and Pi are released

• Cross-bridge then broken as new ATP attaches to myosin head

• Head group moves backwards, ATP is hydrolysed to ADP and Pi
  - Can form cross-bridge with thin filament further along and bend again 

• Binding sites for the myosin head group are covered by tropomyosin subunits
• Myosin cannot bind to these meaning cross-bridges can't be formed and cotnraction cannot occur
• When a action potential arrives, calcium ions are released from the sarcoplasmic reticulum in sarcomeres.
• Calcium ions diffuse through the sarcoplasm and bind to the troponin molecules
• This changes the shape of the troponin
• Tropomyosin moves away from the binding sites on the actin
• Actin-myosin binding sites are uncovered
• Cross-bridges can form
• Results in powerstroke and muscle contraction

Three mechanisms by which ATP supplies are maintained:

• Aerobic respiration in muscle cell mitochondria

• Anaerobic respiration in muscle cell sarcoplasm

• Transfer from creatine phosphate in the muscle cell sarcoplasm